Re: First coil I built worked great !

To: tesla-at-pupman-dot-com
Subject: Re: First coil I built worked great !
From: "Barton B. Anderson" <mopar-at-uswest-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sat, 03 Oct 1998 04:59:03 -0600
Approved: terryf-at-verinet-dot-com
Richie,
First let me say congrats!!! It's always great to hear of a first timer doing
very well in the spark length catgory, or sparks at all for that matter. I
guess the internet is doing ok. Even tonight I am rewriting my "theory" page
on my homepage (got to lose that 1/4 wave stuff - been too complacent the
last few months). Well, 34" spark lengths, in air no less. That's excellent
given the posing power scenario. I too, would be inclinded to hear if anyone
has a hypothesis how you are acheiving these lengths given the relative low
power input based upon bps and hz * 2 firing hepothesis. Your hypothesis of
the cap recharge and refire during a single break may be interesting to
contemplate on your particular system. Can't wait to hear others views.
Again, congrats!!!
Bart

Tesla List wrote:

> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk>
>
> First coil I built worked great !
>
> Hi everybody,  I have just finished building a small (medium) sized
> tesla coil after seeing one demonstrated on an American TV programme
> about lighting.  I am a qualified electrical engineer and have read
> lots of information from the many Internet sites and would like to say
> two things:-
>
> 1. I was very impressed with the performance of my first Tesla Coil.
>
> 2. The information on the Internet sites is VERY good so use it.
>
> The specification of my Tesla Coil is as follows:-
>
> Power supply:           240 VAC, 50 Hz, ? Amps.
> Supply filter:          250 VAC 16 Amp RFI filter.
> Transformer:            2 x 6Kv 100mA Neon Sign Transformers in parallel
>                         (With centre-tapped secondary,  made by
>                         Tunewell transformers of London, England.)
> Primary capacitance:    22 nF Total,  (made of 4 x 22 nF Polyethylene
>                         caps in oil, series/parallel connected.)
> Spark gap:              Static RQ-gap,  5 gaps of roughly 0.5mm each
> Primary Coil:           9.5 Turn Saucer shape spiral inclined at 20
>                         degrees.  Tapped at 7 Turns for biggest sparks.
>                         Overall diameter 450mm
> Secondary Coil:         Roughly 1000 Turns of 0.6mm enamelled wire,
>                         100mm diameter x 700mm length varnished PVC tube.
> Discharge Terminal:     300mm Toroid from 100mm Aluminium vent ducting.
> Operating frequency:    Roughly 250kHz I think.
>
> And now the clincher...
>
> Spark length:           34 inch forked lightning from all around toroid
> Audible noise:          Lots !
>
> The fact is I was impressed with this,  especially when I did some
> calculations about power:-
>
> I know that the primary cap is charging to about 8Kv before the gap
> fires,  because I have tested the gap by charging a capacitor from DC
> until the gap fires.  (It is quite consistant at around 8Kv.)  I have
> calculated the Energy in each bang as follows:
>
>         E = 0.5 * C * V * V
>           = 0.5 * 22n * 8000 * 8000
>           = 0.704 Joules
>
> Assuming the capacitor charges to this value on every half cycle of
> the mains supply,  I figured the power throughput of the capacitor:
>
>         P = Breaks per second * E
>           = 100 * 0.704
>           = 70.4 Watts    <============
>
> Now I know there are losses in capacitors, spark gaps, wiring, coils
> and corona etc.  So I think that not all of this power results in
> secondary sparks.
>
> My point is that the spark length seems high for the relatively low 6Kv
> neon transformers,  small primary capacitor  and LOW CALCULATED POWER !
> I have heard figures like 500 to 1000 Watts per foot mentioned before,
> does anyone have any feelings on this ? (Are my calculations wrong ?)
>
> One thing I do notice is that by changing the primary capacitance or
> by disconnecting one neon transformer I can change the "pitch" of the
> "screeching" noise that the secondary sparks make.  Because the
> screeching sounds at a higher frequency than 100Hz I am wondering if
> my tank cap is charging and discharging several times in each half
> cycle.  Could this be happening with a basic static gap and resulting
> in more than my estimated 100 breaks per second ?  Hence more power ?
>
> I have an oscilloscope and plan to determine the break rate by looking
> at the radiated energy using a loop antenna MANY feet away from the
> running tesla coil.  I will keep you informed,  (if the scope lives !)
>
> I hope I haven't rambled on too much for a first posting !
>
>                                 Cheers,
>
>                                         Richie,
>                                         in sunny Newcastle (England.)
>
> PS.
>     The internet site works just fine,  Chip.
>     (No complaints from me !)